Magnetic telegraphone



Jan. 24,y 1939. c. N. HlcKMA-N MAGNETIQ TELEGRAPHONE Filed Aug. e, 195e 2 shee'tsfsheet 1 Y FIG. /A

FIG. Z-

' lFIG. 3

` NVENTOR By CN; H/CKMAN #MLP Patented Jan. 24, 1939 Y f v 22.114,4,844

Alinielsuzfrrc"i'1 -:LmBarnum: Clarence Hiclrinamdaclrson Heights, Y., asi-v51 PATE ,a

signor to Bell Telephone Laboratoriealncorporated, New-"York, Ni Y., a corporation :off

New York.

appiieauonnugast sfiaas, vserial'fl'b. 9445,27

s claims.

non-magnetic disc having one orA more circular 10 concentric grooves containing suitable magnetic material for receiving the signals to be recorded. The magnetic material is preferably in the form of thin heat treated tape spirallywound in a lo the ends of the tape terminating in the same transverse section of the laminated member.

A record member of this type has several distinct advantages over loops used` heretofore. Because of the larger 20 cross-section of the record member the. signals c may be recorded at much higher levels thereby increasing. the margin over the background noise; the disc may be driven at high speeds without slip and due to the substantially uniform thickness of the" laminated member the "objecs tionable noise produced by the joint in a single loop is eliminated. n

Recording is done by longitudinal magnetization `and the pole tips are preferably mounted x0 above the disc with a small clearance to reducey noise. When severalconcentric grooves are used in the same record, pick-up from adjacent fre` very small time delays whichlare often required;

|5 in high quality signal transmission systemsgand which have 'been obtainable heretofore only by` using expensive electrical delay networks.

for testing or other uses, such as the production m of synthetic music, a single frequency is recorded in each laminated record and higher or lower frequencies may b e readily obtained by correspondingly varying the speed of the disc 'during reproduction. 'I'he preferred methods of `recording i5 these tones, .of eliminating undesired harmonics' (ci. 17a-190g), j

This invention relates to magnetic .telegraphones and the object oik theinvention is a recording and reproducingrsystem of this type l andother features -of the mor y recording and reproducing magnets,

the single klayer rjointed according ,to the invention.v

centric grooves 12,; algerien cntainmgicngffi length of thin recording ltape spirally` Wound t grooves apertures above lthe laminated record" clearly understood irom.tlhe ,v following rdetail de,

scription and thei.accompanyingIdravvlngsfiy C `Whih: ,1 i. ,y w

Fig.,1 is a perspective viewof a` telegraphone j machine according tothe inventiony; .y y i Fig. 24 is a sectional view of. one of the laminated,

record members; f y, y` d Fig. 3,is a detailof thepreferred form of the Fig.f4 is a diagram illustratingthe,eilectLofz g the pole-piece spacing on the amplitud'esljkof the f undesired harmonics in 'a` longitudinal system;` plurality lof layers lling the groove'and having.`

Imonies in a transverse system;L f i Fig. 7 is a schematic of a' 'signal delayfsystem' y In Fig; 1 the disc; ui 'ofjbrass @other uita'bief non-magnetic vmaterial hasv al number" ofjco'nf"` fill the groove as kshown inFigg2'xandrprod ce record member i5 about :one-eighth.inclijvvilek The twoendsbf the spiralarepreferablyvin,*he fj same transverse cross-section so that there is no substantial variation in the eilectivel'widthi'tg f of the laminated member'thr'oughout its length.

The tape used may be lof .carbonsteelvor oi'y any other'suitablematerial `which preferably ligas been i s heat treated to improve its recording -propertiesj` One very satisfactory record of thistype consistsjll fof about 60` layers, of two -`mil tape 50 mils wide secured in a one-'eighth inch groove/*with `shellaey j As shown in Fig.l 3 the recording andv repro'- ducing magnets yhave'laminated"pole-pieces |6Q404 i1. The laminations preferablylhavefyoke por-'ff ji y tions I8, I9 of'diierent lengthsandjare.stacked toform" butt "joints at `2llla'nd '2i inalternat'e` j layers.` The assembly is securedtogetherbygsutf` able meansV such as a clamp V22' with 'the polel46 tips 23,24 at the propery spacing-tortille" participle4 l t lar case as described more fully below. A The sig# When used as a generator of tone frequencies,

nal coils 25, 26 maybe woundin'conical"form as shown to provide vthe maximum number'of turns i since the Asystem operates fwith-the' pole tips`out"50 veme1.,summnma @natascha gw.

cording the shield prevents stray flux from 3l, 3l which are engaged by the spring l2 to lock the arm in position over a selected record member. Accurate adjustment of the pole tips with respect to the record is readily obtained by the screw actual contact with the member they tend to chatter, particularly when high speeds are used, and the consequent variations in the reluctance of the magnetic circuit introduces noise into the reproduction. By adjusting the tips slightly out of contact a relatively high series reluctance is introduced and any superimposed variations in reluctance are relatively small.

The magnetic shield 34 extends beyond the disc Il to a support on the base board 3i and may be rotated by the knob to bring the apertures 31 into line with the arm 21 as required. mring rereaching the record members on either side of the one being magnetized and during reproduction it prevents the field of adjacent recordings from aiecting the reproducing magnets. This makes it practical to make the groove spacing only one inch or less which is an important advantage in cases where a large number of recordings is required in a single machine.

When the invention is used as a delay mechanism the circuit carrying the speech or other signals to be delayed is connected to the amplifier 38 iFig. 7) thereby energizing the recording magnets 39 and magnetizing the record member 40 in the rotating disc 4I. The reproducing magnets 42 subsequently reproduce this record and transmit the signals to the outgoing circuit through the amplifier 43 with a transmission delay directly proportional to the spacing between the two sets of magnets and inversely proportional to the speed of the disc.

When single frequencies are recorded for tone generating purposes it is important that the re- Acording be reentrant, or in other words, that the circumference of the record be an exact multiple of the wave length of the frequency to vbe recorded. Under this condition the magnetization in the record varies cyclically throughout the 'length of the record so that no transients are introduced in any part of the revolution during reproduction. A convenient method of making such records is illustrated in Fig. 6. 'I'he record disc 44 is driven by a synchronous motor 45 at the desired speed and the recording frequencies are obtained from a harmonic generator, such as an overloaded amplier 46, connected to the current source 41 driving the motor. The filter 48 passes current of the harmonic frequency to be recorded to the magnets 49 through the attenuator 50. With the disc 44 rotating, the attenuator is operated to build up currents in the magnets to full recording level and then reduce them in amplitude to zero again. Since the disc is rotating synchronously with the cyclic variations in the frequency beingv recorded, the length in record of a complete cycle of variations in the magnetization will always be proportional to the ratio ofthe speed of the disc to the frequency of the signal recorded. While only multiples of the frequency of thesupply source can be recorded in this manner, any intermediate tone frequency may be obtained by driving the record during reproduction at the proper speed.

In recording tone frequencies the undesired harmonics are suppressed as much as possible, but it is found that the reproduction of the purest single frequency record obtainable contains harmonic components of sufficient magni- 33. 'When the pole tips are in tudetomaketherecordunsuitableforsomepnrposes. Applicant-has discovered that these nndesiredharmonicsmaybesogreatlyredwedin amplitude as to be no longer objectionable by properly spacing the tips-of the pole-pieces of the reproducing magnets.

In Fig. 4, curve Il represents the variations in vmagnetization along a section of the record I2 at the desired tone frequency fs for a given linear record speed. If the pole tips 28, f4 are spaced a distance S equal to one-half the wave-length of frequency fs there will be satisfactory response at this frequency but for the second harmonic 2f@ (curve I3) the spacing is a full wave-length and there will be no response and the same is true of all other even harmonics. For the odd harmonics such as 3f (curve I4) the spacing will be one and a half times the wave-length or more and the response will be much reduced. In general, the spacing should be about one-half the wave-length of the frequency of interest, but due to the relative amplitudes and phase relationships of the harmonics or to some other factor, it. may be found desirable to use a slightly greater or smaller spacing in some cases.

This general method of reducing harmonics is also applicable to systems using perpendicular or transverse magnetization as illustrated in Fig. 5. In such systems the companion pole-pieces are disposed on opposite sides of the record member with the pole tips 5B, 41 in accurate alignment as more fully explained in Patent 1,944,288 granted to applicant January 23, 1934. When the pole tip thickness is equal to one-half the wave-length in the record of the desired tone frequency .fo (curve 58) the response at that frequency will be a maximum, but for even harmonics such as 2f@ (curve Si) the magnetization in the record will be of opposite polarity under different portions of the pole tips and there will 40 be no response. For reasons analogous to those given inconnection with Fig. 4, the odd harmonics will also be reproduced at reduced amplitudes and the exact dimensions for best results in eachcase can be determined readily by experiment.

What is claimed is:

1. A telegraphone record member comprising a plurality of spiral layers of thin magnetic tape secured directly together, the edges of the layers forming a single, annular recording track.

2. A continuous telegraphone record member comprising a disk having a narrow circular recording track of substantially uniform recording properties and cross-sectional area comprising a plurality of spiral turns of thin tape secured directlyv together and forming a laminated recording track.

3. A telegraphone record member comprising a disc having a plurality of spaced concentric circular grooves and a thin tape disposed on edge in a plurality of layers in each groove.

4. In a telegraphone system a movable member, a plurality of recordings in the member, a

l magnetic shield adjacent the surface of the member having an aperture aligned with one of the recordings, and translating magnets cooperating with said recording through the aperture.

5. In a telegraphone system a non-magnetic disc, a plurality of concentric grooves in the disc each containing a telegraphone record member, means for rotating the disc, a stationary magnetic shield disposed in close spaced relation to the disc, apertures in the shield aligned with the record members, and translating magnets co- 5 dinally magnetized teiegraphone record containing only said tone frequency and its harmonics. signal coils and pole-pieces in the coils terminating in pole tips spaced along one side of the record a distance equal to one-half the wave- 10.) length in the record of said tone frequency.

7. Means for generating a substantially pure tone frequency comprising a moving transversely magnetized telegraphone record containing only said tone frequency and its harmonics, signal coils on opposite sides oi' the member and transversely aligned pole-pieces in the coils terminating in opposed pole tips having a thickness equal to one-half the wave-length in the .record of 5 said tone frequency.

8.1 A telegraphone record member comprising a disc having a circular groove of the order of Vg inch wide anda thin magnetic tape disposed in the groove on edge in a plurality of spiral layers 10 to form a single laminated recording track.

CLARENCE N. HICKMAN. 

